The present invention relates generally to a method for detecting a road bank angle being experienced by a moving vehicle. More particularly, the present invention relates to a method for detecting the road bank angle under dynamic lateral operating conditions for use in a motor vehicle having a yaw control system.
Automotive vehicles with braking systems which respond to vehicle conditions as well as driver input have been produced. For example, when a particular yaw rate is desired, as indicated by a driver""s steering wheel operation, if the vehicle is not producing an adequate yaw rate, the braking system of the vehicle may compensate by altering a particular wheel""s speed. This control is dependent on accurate measurement of several vehicle operating conditions. It has been observed that error can be introduced in the control system if the vehicle is operating at a bank angle. Therefore, it is desirable to determine the bias in the various operating condition signals introduced by operating at a bank angle.
U.S. Pat. No. 5,446,658 (""658) addresses the problem of estimating bank angles of a road surface. However, under various operating conditions, the system described in ""658 patent does not have the ability to calculate the road surface bank angle under dynamic lateral operating conditions. Specifically, if the yaw rate for the vehicle changes by more than a predetermined threshold, the previously determined bank angle is assumed as the current bank angle. Of course, it is quite possible for a vehicle to undergo extreme bank angle variation during the period that the yaw rate is not within a predetermined threshold.
U.S. Pat. No. 6,073,065 provides a method for determining a bank angle experienced by a motor vehicle that is robust to dynamic lateral vehicle operations. However, the methodology reaches its limitation during high frequency maneuvers with simultaneous road bank variation. The estimation during dynamic maneuvers may experience some instantaneous errors.
A paper presented by Y. Fukada entitled xe2x80x9cEstimation of Vehicle Slip-Angle With Combination Method of Model Observer and Direct Integrationxe2x80x9d presented at the International Symposium on Advance Vehicle Control in September 1998, addresses the estimation of road bank angle with vehicle slip angle. In this paper, the difference between lateral accelerometer measured on the force and tire model estimated lateral force is used to obtain the road bank angle. However, its accuracy is contingent on the accuracy of the estimated lateral tire force which, in turn depends on the estimated on the road surfaces and lateral velocity. In this approach, the lateral velocity in road bank angle estimation is believed to be, at best, a convoluted process. Also, the accuracy and robustness of such a calculation is suspected.
It would be desirable to provide a method for determining a bank angle being experienced by a motor vehicle that is robust to dynamic lateral vehicle operating conditions under a wide variety of maneuvers.
There is disclosed herein a method for detecting a bank angle experienced by a motor vehicle. The method comprises the steps of:
calculating a first bank angle estimate dependent on said first signal;
providing a second signal corresponding to a yaw rate of the vehicle;
calculating a second bank angle estimate dependent on said second signal;
calculating a third bank angle estimate dependent on both said first and second signals;
calculating a dynamic compensation factor based as a function of said first bank angle estimate, said second bank angle estimate and said third bank angle estimate;
decomposing the third bank angle estimate into a plurality of third bank angle frequency layers;
reducing each of the plurality of third bank angle frequency layers in response to a multiplicative factor, said multiplicative factor being a function of said dynamic compensation factor to obtain a plurality of reduced third bank angles;
calculating a final bank angle bias estimate based on a sum of the plurality of reduced third bank angles.
It is an object of the present invention to provide a method for detecting a bank angle experienced by a vehicle while undergoing transient lateral operation.
Other objects and features of the present invention will become apparent when viewed in light of the detailed description of the preferred embodiment when taken in conjunction with the attached drawings and appended claims.